1. Field of the Invention
The present invention relates to a transparent EMI shielding film, and more particularly, to an EMI shielding/absorbing film having further improved EMI shielding/absorbing performance and light transmission.
2. Discussion of Related Art
In recent years, electromagnetic interference (EMI) has increased rapidly with the trend towards high functionality, high capacity and high performance of various electrical or electronic devices.
The EMI is becoming known as a cause of malfunctioning in the electrical or electronic devices. Therefore, it is necessary to shield and absorb electromagnetic waves generated from the electronic devices to prevent such malfunctioning. To shield and absorb the electromagnetic waves, conductive or magnetic metals, ceramics, or conductive polymers may be used instead of materials including metals, ceramics, and polymers through which the electromagnetic waves do not penetrate. For example, there are methods including making use of a housing made of a metal, inserting a metal plate between circuit boards, or covering a cable with metal foil, etc. Meanwhile, EMI shielding films for display devices require transparency since the EMI shielding films have to allow recognizing what is displayed on a screen. However, since the EMI shielding films cannot have guaranteed transparency due to opaqueness of a conductive layer made of functional particles such as metals, EMI shielding films exhibiting light transmission has been in demand.
Such transparent EMI shielding films are classified into mesh type and conductive film type.
FIG. 1 is a cross-sectional view of a conventional mesh-type EMI shielding film.
Referring to FIG. 1, a conventional mesh-type EMI shielding film 10 has a structure in which a pattern having engraved grooves is formed on a top surface of a transparent substrate 11, and a conductive metal 12 is disposed in the grooves. Since the conductive metal 12 has a very small width, transparency of the EMI shielding film 10 may be maintained overall.
However, the mesh-type EMI shielding film 10 has a problem in that it has very low level of light transmittance when the conductive metal 12 required to exhibit a sufficient shielding property is printed with an ink or paste in the form of a polymer complex. Also, the mesh-type EMI shielding film 10 has limits in the thickness due to a printing problem of the conductive metal 12 and thus has limitations in enhancing shielding performance. Also, a method of forming a mesh plating layer of silver, copper, or the like using a plating method to enhance conductivity of the conductive metal with a small thickness may be applied to significantly improve electrical conductivity of the conductive metal and enhance EMI shielding ability, there is a problem in that the process is complicated and not environmentally friendly.
FIG. 2 is a cross-sectional view of a conventional conductive film-type EMI shielding film.
Referring to FIG. 2, a conventional conductive film-type EMI shielding film 20 has a structure in which a thin conductive film 23 is disposed on a transparent substrate. The conductive film 23 has a sufficiently small thickness not to impair overall transparency of the EMI shielding film 20. For example, the conductive film 23 may be formed of nanowires.
The conductive film-type EMI shielding film 20 has a drawback in that the thickness of the conductive film 23 may need to be increased excessively to realize a sufficient shielding property, and thus light transmission may be degraded. Also, when the thickness of the conductive film 23 is made too small for light transmission, a conductive network may be disconnected and result in a degraded shielding property. In particular, when silver nanowires which have been used as a material for conductive films are applied to display devices such as touch screens, haze may be increased and contrast may be lowered.
Therefore, there is a demand for transparent EMI shielding/absorbing films capable of exhibiting sufficient EMI shielding performance while simultaneously maintaining the light transmission.